1. Field of the Invention
The present invention relates generally to batteries and, more particularly, to decreasing battery terminal contact resistance attributable to the presence of an insulating contaminant layer on the battery terminals.
2. Related Art
Electrical devices commonly derive their power by way of one or more batteries that are housed within a compartment associated with the electrical device. The battery compartment typically is integral with the electrical device. Alternatively, the battery compartment can be provided remotely from the electrical device with a connection thereto via conductor elements such as electrical wires.
There are numerous types of primary (non-rechargeable) and secondary (rechargeable) batteries. Dry cell batteries are commercially available in a number of well-known sizes and configurations such as the standardized AAA, AA, C, and D battery sizes. Miniature batteries, also referred to as watch, disc, dish, and button batteries, are also available in standard sizes and are commonly used in hearing aids, electric wristwatches and other devices.
Dry cell battery compartments have a positive contact, commonly in the form of a planar tab or a conical coiled spring, for electrically contacting the negative terminal of an installed dry cell battery. A negative contact, commonly in the form of a planar tab, is provided in the compartment for electrically contacting the positive terminal of an installed dry cell battery. Planar and dimpled tabular contacts are commonly used in miniature battery compartments. When one or more batteries are installed in such battery compartments, the device serves as an electrical load placed across the terminals of the installed batteries.
In compartments that require more than one dry cell battery, the batteries are housed in a series or parallel arrangement. In a series arrangement, the batteries are positioned xe2x80x9chead to tailxe2x80x9d with the planar surface of the positive terminal button abutting the negative terminal surface of the forward adjacent battery, with the batteries having parallel or coexistent longitudinal axes; that is, the batteries form a straight line. As a result, batteries arranged in this manner are said to be xe2x80x9clinearly alignedxe2x80x9d.
A well-documented problem with standard dry-cell, miniature and other types of batteries is the oxidation and sulfidation of the battery terminals. Oxide and sulfide layers often develop with time such as from when the batteries are manufactured to when they are ultimately used. In addition, galvanic corrosion of the battery terminals can occur in certain circumstances and environments. These oxide, sulfide and corrosive films are surface contaminants that insulate the battery terminal. Of particular relevance to the present invention is the increased battery contact resistance caused by this insulating contaminant layer. Contact resistance is the electrical resistance in the battery circuit attributable to the physical contact between adjacent batteries and between the batteries and the device. In circumstances in which the terminals have an insulting contaminant layer, the contact resistance can be significant, consuming valuable battery power, particularly in high current applications. This results in the rapid depletion of the installed batteries, decreasing device availability and increasing the rate at which the batteries need to be replaced or recharged. Furthermore, such a high contact resistance decreases the maximum current available from the installed batteries, making certain battery arrangements unsuitable for use in high current devices.
For example, two 1.2-volt dry cell batteries arranged in series provide 2.4 volts. In a high current application of 5 amperes, the batteries deliver 12 watts of power. If the contact resistance increases from a nominal 0.06 ohms to 0.2 ohms due the presence of an insulating contaminant layer on one or more of the battery terminals, the power consumed overcoming the contact resistance increases from 1.5 to 5 watts. In other words, 40% of the available power is consumed by the contact resistance. This reduces the power and current available to the device. In addition, the lost power essentially heats the battery terminals and/or device contacts. This can damage or degrade the batteries, damage the battery compartment and increase the risk of fire.
One traditional approach to solving this problem has been to provide the operator with a separate dimpled piece of sheet metal to insert between neighboring linearly aligned batteries. This approach has some drawbacks. For example, the additional part increases product cost. It also adds complexity, making it difficult for the user to install quickly and easily the batteries. The user must install a first battery, position the sheet metal intermediate contact in the proper position, and then insert the second battery while retaining the sheet metal in its proper position. Thus, such supplemental parts are often used improperly or misplaced or lost and not used at all.
An insulating contaminant layer on the battery terminal also increases the contact resistance between the batteries and device. For example, the first battery in a series battery arrangement is positioned with the planar surface of its positive terminal button parallel to and in contact with a planar negative tab contact of the device. The last battery in the series battery arrangement is positioned such that its planar negative terminal surface is parallel to and in contact with a planar conical coiled spring winding or contact tab. Conventional conical coiled spring contacts have a series of helical windings, with the upper winding residing in a plane substantially parallel to and in contact with the negative battery terminal surface. Similarly, in parallel arrangements, the batteries are each positioned with their positive and negative terminals contacting the opposing polarity contacts of the battery compartment in a similar manner. The planar tab and planar conical coiled spring winding can not penetrate the insulating contaminate layer coating the battery terminals.
The present invention is directed to a conical coiled spring battery contact for use in a battery compartment that ruptures an insulating contaminant layer on a terminal of a battery installed in the battery compartment. Such a conical coiled spring contact minimizes the contact resistance between the conical coiled spring contact and the battery terminal due to the presence of such an insulating contaminant layer. This in turn increases the amount of battery power and current available for the implementing device.
A number of aspects of the invention are summarized below, along with different embodiments that may be implemented for each of the summarized aspects. It should be understood that the embodiments are not necessarily inclusive or exclusive of each other and may be combined in any manner that is non-conflicting and otherwise possible regardless of which aspect of the invention they are presented in connection with. It should also be understood that these summarized aspects of the invention are exemplary only and are considered to be non-limiting.
In one aspect of the invention, a conical coiled spring contact for use in a battery compartment is disclosed. The coiled spring contact is constructed and arranged such that only a battery terminal contact point contacts an abutting a terminal of a battery installed in the battery compartment, wherein said contact point is defined by a minimal surface area of an upper end turn of the coiled spring contact.
In another aspect of the invention, a conical coiled spring contact for use in a battery compartment to contact a terminal of a battery installed in the battery compartment is disclosed. The conical coiled spring contact is constructed and arranged with an upper end turn configured such that a minimum surface area of the upper end turn comes into contact with the installed battery.
In a still further aspect of the invention, a battery compartment is disclosed. The battery compartment includes a housing configured to receive one or more batteries; and a conical coiled spring contact. The conical coiled spring contact has a lower end turn secured to an interior surface of the housing, an upper end turn for contacting a terminal of an installed battery, and a plurality of concentric windings disposed between the upper and lower end turns. The upper end turn forms a forward-most eccentric terminal contact point to contact a terminal of a battery installed in the housing.